This proposed project is a randomized clinical trial testing whether supplementation with selenium and/or vitamin E affects pulmonary function. There is compelling evidence from observational epidemiologic studies that high antioxidant intakes are associated with reduced risks of chronic obstructive disease (COPD) and increased lung function. This proposal is an ancillary study to the multisite selenium and Vitamin E Cancer Prevention Trial (SELECT), a 4-arm placebo-controlled, double-blinded randomized trial in 32,400 men testing whether daily supplementation with vitamin E (400mg alpha-tocopherol), selenium (200 micrograms selenomethionine) or both vitamin E and selenium can prevent prostate cancer. We will enroll 3,000 SELECT participants for this respiratory ancillary study, and extend data collection to include pulmonary function, respiratory disease, and respiratory symptoms. We also will collect biological measures of nutrient exposure (serum vitamin E and selenium) and plasma lipids (total and high-density lipoprotein cholesterol) on all participants and oxidant burden (urinary F2-isoprostane) on a sub sample of heavy smokers and men with COPD. The primary outcome will be change between baseline and year 3 in forced expiratory volume in the first second (FEV1). FEV1 is a valid and reliable measure of respiratory function that strongly predicts COPD and mortality. Extensive data on diet and dietary supplement use are being collected by the SELECT parent study. All specific aims examine pre-specified contrasts between the 4 arms of the SELECT randomized trial. The underlying hypothesis is that antioxidants will reduce the age related decline in FEV1, and thus at the 3-year follow-up FEV1 will be higher in the groups receiving antioxidant supplements compared to controls. A secondary aim considers whether the effect of supplementation is greater among smokers (high burden of exogenous oxidants) who, by purposive selection of the study sites, will comprise 25% of the sample. The proposed study addresses important and timely questions about diet and lung disease, and makes cost efficient use of the research infrastructure of SELECT. This study could have enormous public health significance, because supplementation with antioxidant nutrients would be an inexpensive and practicable means to reduce morbidity and mortality from pulmonary disease.